An upgrade to a system is backwards compatible if the upgrade does not render the old version of the system unusable.

Base58 is an encoding scheme with an alphabet of 58 characters, including upper and lowercase letters A-Z and the digits 1-9. A variant of Base58 called Base58Check is used to represent legacy Bitcoin addresses.

Base64 is an encoding scheme used to encode Partially Signed Bitcoin Transactions (PSBTs). The Base64 alphabet uses 64 characters.

Batching involves consolidating multiple payments into a single transaction with many outputs. This can help senders save on fees, which are paid based on how much data their transaction uses.

Bech32 is an encoding scheme used to encode SegWit addresses and lightning invoices. The Bech32 alphabet contains 32 characters.

Binary is a number system that only uses two numbers: ones and zeros. Computers operate in binary, meaning they store data and perform calculations using only ones and zeros.

A bit is short for “binary digit”, and is either a one or a zero. Bits are the atomic unit of digital data. All computer data is stored as bits, which are grouped into sets of eight, and called bytes.

Bitcoin is the world’s first decentralized digital currency that operates without a central authority and has a scarce supply. Bitcoin uses a peer-to-peer network, meaning no permission or middle man is required to send, store, or receive bitcoin.

Bitcoin Core is the reference implementation for the Bitcoin source code, meaning all other implementations look to Core for guidance. Bitcoin Core was started by Satoshi Nakamoto when they released the first version of Bitcoin's source code.

A Bitcoin Improvement Proposal (BIP) is a formal proposal to change Bitcoin. Upgrades, security improvements, industry standards, and more all begin as BIPs.

Bitcoin-Qt is the name of the graphical user interface or GUI which comes as part of the Bitcoin Core software package.

Bitcoind is the name of the software service that runs a Bitcoin node and wallet. This service comes with Bitcoin Core’s software and is used by most nodes on the network.

A block is a collection of transactions that occur on the Bitcoin network. Blocks are linked together chronologically to form a blockchain.

A block explorer is a software application that allows anyone to easily browse or query the blockchain.

A block header contains the metadata about a block of transactions. The block header, not the entire block, is what is actually being hashed to produce the Proof-of-Work.

Beginning at zero with the genesis block, all blocks are numbered in ascending order. This number is known as a block’s height. The current block height is simply the number of blocks in a given blockchain minus one.

The block reward is a combination of the block subsidy (newly minted bitcoin) and all transaction fees paid by transactions in a block. The block reward is collected by miners in the coinbase transaction.

The block size describes the amount of data which a block is allowed to take up, measured in bytes. Miners are not allowed to create a block with more data than the block size limit allows for.

The block subsidy is the amount of new bitcoin minted in each block, and it forms the largest part of the block reward. The block subsidy is cut in half every four years.

Block weight is a measure of the size of a block, measured in weight units. The Bitcoin protocol limits blocks to 4 million weight units, equivalent to a maximum of 4 megabytes.

A blockchain is a chronological list of records, called blocks. Each of these blocks contains transactions. Once a block is added to the blockchain, it is infeasible to alter, giving Bitcoin its immutability.

A brokerage is a financial institution which allows its customers to buy assets directly.

BTC is the ticker symbol for Bitcoin. A bitcoin (1 BTC) is divisible into 100 million (100,000,000) sats.

A byte is a string of eight zeros and ones, or bits. Bytes are usually represented in hexadecimal notation, not as binary. One thousands bytes form a kilobyte (kB), and one million bytes forms a megabyte (MB).

The Byzantine Generals Problem describes the difficulty decentralized parties have in trustlessly establishing consensus.